U.S. patent number 10,075,037 [Application Number 15/033,681] was granted by the patent office on 2018-09-11 for electric motor and electric power steering device using the same.
This patent grant is currently assigned to Mitsubishi Electric Corporation. The grantee listed for this patent is Mitsubishi Electric Corporation. Invention is credited to Satoru Akutsu, Takanori Ichikawa, Yoshihiko Onishi, Yuji Takizawa.
United States Patent |
10,075,037 |
Ichikawa , et al. |
September 11, 2018 |
Electric motor and electric power steering device using the
same
Abstract
An electric motor includes a cylindrical holder mounted to an
end of a rotation shaft, a sensor magnet mounted to the holder, and
a rotation sensor mounted at a position at which the rotation
sensor opposes the sensor magnet in a direction of an axis of
rotation and detecting a rotating field of the sensor magnet. The
end of the rotation shaft has a cylindrical shape with a
non-circular cross section formed of at least one plane and a
curved surface in an outer peripheral portion. At least one of an
inner peripheral portion and an outer peripheral portion of the
holder forms a non-circular cross section formed of a plane
parallel to the axis of rotation and a curved surface connected to
the plane. The plane of the rotation shaft and the plane of the
holder are parallel to each other and the curved surface of the
rotation shaft and the curved surface of the holder are in contact
with each other.
Inventors: |
Ichikawa; Takanori (Tokyo,
JP), Akutsu; Satoru (Tokyo, JP), Onishi;
Yoshihiko (Tokyo, JP), Takizawa; Yuji (Tokyo,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Mitsubishi Electric Corporation |
Tokyo |
N/A |
JP |
|
|
Assignee: |
Mitsubishi Electric Corporation
(Tokyo, JP)
|
Family
ID: |
54143968 |
Appl.
No.: |
15/033,681 |
Filed: |
March 19, 2014 |
PCT
Filed: |
March 19, 2014 |
PCT No.: |
PCT/JP2014/057547 |
371(c)(1),(2),(4) Date: |
May 02, 2016 |
PCT
Pub. No.: |
WO2015/140961 |
PCT
Pub. Date: |
September 24, 2015 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20160285331 A1 |
Sep 29, 2016 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01D
11/245 (20130101); H02K 1/02 (20130101); G01B
7/30 (20130101); H02K 11/215 (20160101); B62D
5/04 (20130101); H02K 1/28 (20130101); G01D
5/145 (20130101); G01D 5/24423 (20130101); H02K
7/003 (20130101); H02K 29/08 (20130101) |
Current International
Class: |
H02K
1/28 (20060101); G01B 7/30 (20060101); G01D
5/14 (20060101); H02K 11/215 (20160101); B62D
5/04 (20060101); H02K 1/02 (20060101); G01D
5/244 (20060101); G01D 11/24 (20060101); H02K
7/00 (20060101); H02K 29/08 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
|
203313003 |
|
Nov 2013 |
|
CN |
|
62-135564 |
|
Aug 1987 |
|
JP |
|
5-316705 |
|
Nov 1993 |
|
JP |
|
6-62784 |
|
Sep 1994 |
|
JP |
|
2005-318687 |
|
Nov 2005 |
|
JP |
|
4230958 |
|
Feb 2009 |
|
JP |
|
2010-93869 |
|
Apr 2010 |
|
JP |
|
2013-7731 |
|
Jan 2013 |
|
JP |
|
Other References
Communication dated Dec. 6, 2016, issued by the Japan Patent Office
in corresponding Japanese Application No. 2016-508397. cited by
applicant .
Communication dated Oct. 25, 2017, from the European Patent Office
in counterpart application No. 14885856.6. cited by applicant .
International Search Report of PCT/JP2014/057547, dated May 27,
2014. [PCT/ISA/210]. cited by applicant .
Communication dated Jan. 29, 2018, from State Intellectual Property
Office of the P.R.C. in counterpart application No. 201480077236.3.
cited by applicant.
|
Primary Examiner: Le; Dang
Attorney, Agent or Firm: Sughrue Mion, PLLC Turner; Richard
C.
Claims
The invention claimed is:
1. An electric motor comprising; a rotation shaft; a rotor mounted
to the rotation shaft; a stator mounted so as to oppose an outer
peripheral surface of the rotor; a cylindrical holder mounted to an
end of the rotation shaft; a sensor magnet mounted to the holder;
and a rotation sensor mounted at a position at which the rotation
sensor opposes the sensor magnet in a direction of an axis of
rotation and detecting a rotating field of the sensor magnet;
wherein the end of the rotation shaft where the holder is mounted
has a cylindrical shape with a non-circular cross section formed of
at least one plane and a curved surface in an outer peripheral
portion; at least one of an inner peripheral portion and an outer
peripheral portion of the holder forms a non-circular cross section
formed of a plane parallel to the axis of rotation and a curved
surface connected to the plane; the plane of the rotation shaft and
the plane of the holder are parallel to each other and the curved
surface of the rotation shaft and the curved surface of the holder
are in contact with each other; and the sensor magnet is integrally
molded with the holder continuously from an inside of the holder to
an outside of the holder through a hole provided on an end face of
the holder.
2. The electric motor according to claim 1, wherein the sensor
magnet is integrally molded with the holder at one end and fixedly
supported at the one end.
3. The electric motor according to claim 2, wherein the holder is
provided with at least one hole in a portion where the sensor
magnet is integrally molded.
4. An electric power steering device, comprising the electric motor
set forth in claim 3.
5. An electric power steering device, comprising the electric motor
set forth in claim 2.
6. The electric motor according to claim 1, wherein the sensor
magnet and the rotation shaft have a gap in a direction of the axis
of rotation via the holder.
7. An electric power steering device, comprising the electric motor
set forth in claim 6.
8. The electric motor according to claim 1, wherein the holder is
made of a non-magnetic material.
9. An electric power steering device, comprising the electric motor
set forth in claim 8.
10. The electric motor according to claim 1, wherein the sensor
magnet is shaped substantially like a cylindrical pillar with
planes at both ends.
11. An electric power steering device, comprising the electric
motor set forth in claim 10.
12. The electric motor according to claim 1, wherein the sensor
magnet is an isotropic magnet having a residual flux density of 0.4
to 0.8 [T].
13. An electric power steering device, comprising the electric
motor set forth in claim 12.
14. The electric motor according to claim 1, wherein the planar
portion provided to the outer peripheral portion of the holder and
a plane of a fit portion for the rotation shaft are parallel each
other.
15. An electric power steering device, comprising the electric
motor set forth in claim 14.
16. The electric motor according to claim 1, wherein the holder has
a protrusion, which is a part of the holder protruding in the
direction of the axis of rotation from an end face of the sensor
magnet on a side opposing the rotation sensor.
17. An electric power steering device, comprising the electric
motor set forth in claim 1.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a National Stage of International Application
No. PCT/JP2014/057547 filed Mar. 19, 2014, the contents of all of
which are incorporated herein by reference in their entirety.
TECHNICAL FIELD
The present invention relates to an electric motor for vehicle and
an electric power steering device using the same.
BACKGROUND ART
An electric motor in the related art includes a sensor magnet and a
cover member fixed to an end of a rotation shaft and covering at
least a part of the end. The cover member has a holder located
outside of an end face at the end of the rotation shaft. The holder
includes a space portion with a non-circular cross section that
extends in a direction of an axis of rotation of the rotation
shaft. An outer shape of the sensor magnet is of a non-circular
shape formed so as to conform to the sectional shape of the space
portion. Hence, rotations of the sensor magnet about the axis of
rotation are regulated by inserting the sensor magnet into the
space portion (as is described, for example, in PTL 1).
In another electric motor in the related art, an end of the
rotation shaft is of a non-circular shape having at least one
planar portion and the sensor magnet is provided with an attachment
hole of a non-circular shape same as the non-circular shape of the
end of the rotation shaft. The sensor magnet is mounted to the
rotation shaft by loose-fitting. Herein, rattling in the mount
portions is suppressed by inclining the sensor magnet with respect
to the rotation shaft until a part of the sensor magnet makes
contact with the rotation shaft (as is described, for example, in
PTL 2).
CITATION LIST
Patent Literatures
PTL 1: JP-A-2010-93869
PTL 2: Japanese Patent No. 4230958
SUMMARY OF INVENTION
Technical Problem
When the mount portions of the cover member and the rotation shaft
are of a circular shape as in PTL 1, there is no positioning
portion in a rotation direction of the electric motor. Accordingly,
an angular error between the sensor magnet and a rotor magnet
deteriorates detection accuracy of a rotation angle of the motor.
An electric power steering device equipped with such an electric
motor therefore fails to generate an adequate assist torque and has
a problem that steering feeling becomes poor. Herein, because the
sensor magnet and a groove in the holder are of a non-circular
shape, rotations of the sensor magnet about the axis of rotation
can be regulated. However, because fit portions of the holder and
the rotation shaft are of a circular shape, rotations of the holder
about the axis of rotation cannot be regulated. Accordingly,
angular displacement occurs between the sensor magnet and the rotor
angle when the holder slides in the rotation direction. Hence, the
same problem as described above also occurs. Further, because the
holder is in contact with and fixed to the end face of the rotation
shaft, a clearance between the sensor magnet and the rotation
sensor disposed oppositely to the sensor magnet in close proximity
varies considerably due to an integrated tolerance of motor parts,
and detection accuracy becomes unstable. In order to reduce a
variation, a tolerance between parts has to be reduced, which
causes an increase of the manufacturing costs.
The electric motor in the electric power steering device for
vehicle has to be lightweight in order to improve fuel efficiency
of the vehicle and also has to assist the steering with an adequate
steering torque by detecting a rotation angle of the electric motor
correctly. That is to say, when the number of parts forming the
electric motor is increased, there arises a problem that fuel
efficiency of the vehicle becomes poor, and when a rotation angle
of the electric motor cannot be detected correctly, there arises a
problem that the steering becomes difficult. Further, because the
electric power steering device is installed to hundreds of
thousands to millions of vehicles, it goes without saying that the
electric motor has to be made of simple materials, easy to process,
easy to assemble, and inexpensive by reducing the material costs,
the processing costs, and the assembly costs. The motor of PTL 1 is
disadvantageous to reduce the weight and the costs for the
following reasons: the holder used as a magnet cover is made of
brass and formed in a complex shape provided with a polygonal hole
and a circular hole; the sensor magnet is made of expensive
rear-earth materials sintered at high density (that is, the sensor
magnet is more expensive and heavier than a typical resin-molded
magnet); and another member, such as an elastic member, is required
when the holder and the sensor magnet are fixed without using an
adhesive.
When the hole provided to the sensor magnet and the rotation shaft
are directly mounted as in the motor of PTL 2, positional accuracy
of the sensor magnet depends on molding accuracy of the magnet.
However, molding accuracy is low in comparison with mechanical
processing. Hence, positional accuracy of the sensor magnet and the
rotor magnet is also deteriorated and so is detection accuracy of a
rotation angle of the motor. The steering feeling therefore becomes
poor. In addition, because the sensor magnet is mounted to the
rotation shaft by inclining the sensor magnet, a clearance between
the sensor magnet and a rotation angle detector differs from one
rotation position to another and a magnetic flux becomes
inhomogeneous. Because detection accuracy of a rotation angle
differs from one rotation position to another, the steering feeling
becomes poor. Further, rotations of the sensor magnet about the
axis of rotation are regulated by fitting the non-circular portions
of the sensor magnet and the rotation shaft. However, when an
external force is applied to the magnet as a molded article,
breaking or chipping may possibly occur. Hence, there arises a
problem that the product quality is deteriorated considerably.
Because the holder is in contact with and fixed to the end face of
the rotation shaft, an integrated tolerance of the motor parts
makes a clearance between the rotation sensor and the sensor magnet
vary considerably. Detection accuracy thus becomes instable. In
order to reduce such a variation, a tolerance between the parts has
to be reduced, which causes an increase of the manufacturing costs.
In addition, because the motor of PTL 2 requires a washer, which is
a member different from the holder, this motor is disadvantageous
to reduce the weight and the costs.
The invention was devised to solve the problems discussed above and
has an object to obtain an electric motor and an electric power
steering device with good steering performance and high reliability
by enhancing detection accuracy of a rotation angle of the electric
motor and by mounting a sensor magnet to a holder or a rotation
shaft at high strength with a simple structure.
Solution to Problem
Each of an electric motor and an electric power steering device of
the invention includes: a rotation shaft; a rotor mounted to the
rotation shaft; a stator mounted so as to oppose an outer
peripheral surface of the rotor; a cylindrical holder mounted to an
end of the rotation shaft; a sensor magnet mounted to the holder;
and a rotation sensor mounted at a position at which the rotation
sensor opposes the sensor magnet in a direction of an axis of
rotation and detecting a rotating field of the sensor magnet. The
end of the rotation shaft where the holder is mounted has a
cylindrical shape with a non-circular cross section formed of at
least one plane and a curved surface in an outer peripheral
portion. At least one of an inner peripheral portion and an outer
peripheral portion. of the holder forms a non-circular cross
section formed of a plane parallel to the axis of rotation and a
curved surface connected to the plane. The plane of the rotation
shaft and the plane of the holder are parallel to each other and
the curved surface of the rotation shaft and the curved surface of
the holder are in contact with each other.
Effects of Invention
According to the invention configured as above, positioning
accuracy of the sensor magnet and the rotation shaft can be
secured. Consequently, detection accuracy of a rotation angle of
the electric motor can be enhanced. In addition, because the planar
portions of the holder and the rotation shaft engage with each
other, rotations of the sensor magnet about the axis of rotation
can be suppressed.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a block diagram of an electric power steering device
according to a first embodiment of the invention.
FIG. 2 is a sectional view of the electric power steering device
according to the first embodiment of the invention.
FIG. 3 is a plan view of a holder according to the first embodiment
of the invention along with a sectional view taken along the line
A-A.
FIGS. 4A and 4B are plan views of a sensor magnet assembly
according to the first embodiment of the invention each along with
a sectional view taken along the line A-A.
FIG. 5 is a plan view of a mount portion of the sensor magnet
assembly and a rotation shaft according to the first embodiment of
the invention along with a sectional view taken along the line
A-A.
FIG. 6 is a plan view showing dimensions of the holder and the
rotation shaft according to the first embodiment of the
invention.
FIG. 7 is a plan view of the sensor magnet assembly and the
rotation shaft according to the first embodiment of the invention
along with a sectional view taken along the line A-A when the
sensor magnet assembly and the rotation shaft are fixed by
press-fitting.
FIG. 8 is a sectional view showing the holder according to the
first embodiment of the invention when a part of the holder is
caulked.
FIG. 9 is a plan view of the sensor magnet assembly and the
rotation shaft according to the first embodiment of the invention
along with a sectional view taken along the line A-A when the
sensor magnet assembly and the rotation shaft are fixed with an
adhesive.
FIG. 10 is a plan view of a sensor magnet assembly according to a
second embodiment of the invention along with a sectional view
taken along the line A-A.
FIG. 11 is a plan view of another sensor magnet assembly according
to the second embodiment of the invention along with a sectional
view taken along the lane A-A.
FIG. 12 is a plan view of a sensor magnet assembly according to a
third embodiment of the invention along with a sectional view taken
along the line A-A.
DESCRIPTION OF EMBODIMENTS
Hereinafter, preferred embodiments of an electric motor and an
electric power steering device of the invention will be described
with reference to the accompanying drawings.
First Embodiment
FIG. 1 is a block diagram of an electric power steering device 100
according to a first embodiment of the invention.
Referring FIG. 1, the electric power steering device 100 includes a
steering wheel 1 operated by a driver, an electric motor 2
assisting the steering by outputting a torque to the steering wheel
1, a reduction device 3 reducing a rotation speed of the electric
motor 2, a control device 4 controlling the driving of the electric
motor 2, a battery 5 supplying a current to drive the electric
motor 2, a torque sensor 6 detecting a steering torque of the
steering wheel 1, a power connector 7 electrically connecting the
battery 5 and the control device 4, a vehicle-side signal connector
8 receiving an input of vehicle-side signals, such as a vehicle
travel speed signal, from the vehicle, and a torque sensor
connector 9 electrically connecting the torque sensor 6 and the
control device 4.
A configuration of the electric motor 2 will be described
first.
The electric motor 2 is a three-phase brushless motor and includes
a stator 11 having an armature winding 10 made up of a phase U, a
phase V, and a phase U, and a rotor 24 (see FIG. 2) positioned
oppositely to the stator 11 in a radial direction and described
below. The armature windings 10 of the stator 11 can adopt either a
Y-connection configuration or a .DELTA.-connection configuration.
Herein, the Y-connection configuration is shown.
A configuration of the control device 4 will now be described.
The control device 4 includes semiconductor switching elements 12a,
such as FETs, switching a motor current according to magnitude and
a direction of an assist torque outputted to the steering wheel 1,
semiconductor switching elements 12b, such as FETs, forming a
power-supply relay as switching means for passing and interrupting
a battery current supplied from the battery 5 to the semiconductor
switching elements 12a, shunt resistors 13 to detect the motor
current, a smoothing capacitor 14 to absorb a ripple component of
the motor current flowing to the electric motor 2, a power circuit
33 described below on which the shunt resistors 13 and the
semiconductor switching elements 12a and 12b are mounted, a coil 15
preventing electromagnetic noises generated at switching actions of
the semiconductor switching elements 12a from flowing to an
outside, a rotation sensor 16 detecting a rotation angle of the
rotor 24 described below, a sensor board 17 on which the rotation
sensor 16 is mounted, a microcomputer 18 computing an assist torque
on the basis of a steering torque signal from the torque sensor 6
and computing a current comparable to the assist torque on the
basis of the feedback of the the motor current and the rotation
angle of the rotor 24 detected in the rotation sensor 16, a drive
circuit 19 outputting drive signals to control operations of the
semiconductor switching elements 12a according to a command from
the microcomputer 18, and a control board 20 on which the
microcomputer 18 and the drive circuit. 19 are mounted.
The microcomputer 18 receives inputs of a steering torque from the
torque sensor 6, rotation angle information of the rotor 24 from
the rotation sensor 16, and a travel speed signal from the
vehicle-side communication connector 8. The microcomputer 18 also
receives an input of the motor current fed back from the shunt
resistors 13. On the basis of these information and signals, the
microcomputer 18 generates a command of rotation direction for
power steering and a current control amount comparable to the
assist torque, and inputs respective drive signals into the drive
circuit 19.
Upon input of the command of rotation direction and a current
control amount, the drive circuit 19 generates drive signals which
are applied to the semiconductor switching elements 12a.
Consequently, a current flows from the battery 5 to the electric
motor 2 via the power connector 7, the coil 15, and the
semiconductor switching elements 12b and 12a. Hence, a desired
amount of assist torque flows in a desired direction. A motor
current detected through the shunt resistors 13 in this instance is
fed back to the microcomputer 18. The motor current is thus
controlled to agree with the motor current command sent from the
microcomputer 18 to the drive circuit 19. Also, the motor current
is controlled after a ripple component generated when the
semiconductor switching elements 12 are driven to switch is
smoothed in the smoothing capacitor 14.
A structure of the electric power steering device 100 will now be
described with reference to FIG. 2. FIG. 2 is a sectional view of
the electric power steering device 100 of the first embodiment.
A structure of the electric motor 2 will be described first.
The electric motor 2 includes a rotation shaft 21, bearings 22a and
22b on which the rotating shaft 21 is supported in a rotatable
manner, the rotor 24 to which multiple magnetized rotor magnets 23
are fixed in a circumferential direction, the stator 11 provided so
as to oppose an outer peripheral surface of the rotor 24, a frame
25 to which the stator 11 is fixed, a housing 26 connected to one
end of the frame 25 and to which the bearing 22a is mounted, a
coupling 27 fixed to an end of the rotation shaft 21 and
transmitting a torque of the electric motor 2, and a sensor magnet
assembly 200 formed of a magnetized sensor magnet 28 and a holder
29 integrated into one unit and attached to an end of the rotation
shaft 21 on an opposite side to the end where the coupling 27 is
fixed.
The stator 11 is formed, for example, by fixing 0.3 to 0.5-mm-thick
magnetic steel sheets (not shown) laminated in a direction of an
axis of rotation of the electric motor 2 by die-cutting caulking or
welding. The stator 11 also includes an insulator 30 inserted among
magnetic-pole teeth not shown) facing an outer periphery of the
rotor magnets 23 disposed along the outer periphery of the rotor
24, and the armature winding 10 wound around the insulator 30 and
connected to the three phases U, V, and W. Winding terminals of the
armature winding 10 extend parallel to the direction of the axis of
rotation of the electric motor 2 toward the control device 4
(rightward in the drawing) and connect to output terminals of the
phases U, V, and W. The frame 25 having a mount portion for the
stator 11 is disposed in an outer peripheral portion of the stator
11. The stator 11 is mounted to the frame 25, for example, by
thermal insert or press-fitting. The stator 11 is thus fixed.
As with the stator 11, the rotor 24 is formed, for example, by
fixing 0.3 to 0.5-mm-thick magnetic steel sheets (not shown)
laminated in the direction of the axis of rotation of the electric
motor 2 by die-cutting caulking or welding. For example, when the
rotor 24 adopts an SPM (Surface Permanent Magnet) structure, the
rotor magnets 23 formed of a permanent magnet are fixed along the
outer periphery of the rotor 24 with an adhesive or the like. The
rotor magnets 23 are magnetized before or after the rotor magnets
23 are fixed to the rotor 24.
The frame 25 is provided with mount portions for the stator 11 and
the bearing 22b. The stator 11 is mounted to the frame 25, for
example, by press-fitting or thermal insert, and the bearing 22b is
mounted to the frame 25, for example, by press-fitting. Each of the
stator 11 and the bearing 22b is thus fixed to the frame 25. An end
face of the frame 25 is provided with fit portions for the housing
26 and a heat sink 32 described below. The end face is processed at
a high degree of accuracy to secure positional accuracy of
respective parts.
The housing 26 includes a mount portion for the bearing 22a. The
bearing 22a is mounted to the housing 26, for example, by
press-fitting or thermal insert, and is thus fixed. The housing 26
also includes a fit portion for the end face of the frame 25. The
fit portion and one end of the frame 25 are fit together and fixed
with screws 31. In order to secure air-tightness in the electric
motor 2, a seal member, such as an O-ring (not shown) and an
adhesive (not shown), is applied to the the fit portions of the
housing 26 and the frame 25.
The coupling 27 is fixed at one end of the rotation shaft 21 by,
for example, press-fitting and transmits a drive force to a
transmission mechanism (riot shown) of the electric power steering
device 100. The rotation shaft 21 is allowed to rotate when both
ends are fit to the bearings 22a and 22b. At one end fit to the
bearing 22b, the rotation shaft 21 has a fit portion 36a for the
sensor magnet assembly 200 described below. As has been described,
the sensor magnet assembly 200 is formed of the holder 29 and the
sensor magnet 28. The sensor magnet 28 is mounted so as to oppose
the rotation sensor 16 described below in the direction of the axis
of rotation.
A structure of the control device 4 will now be described.
The control device 4 controlling the driving of the electric motor
2 is disposed on the axis of rotation of the electric motor 2. The
control device 4 includes the heat sink 32 dissipating heat
generated in the respective parts, the power circuit board 33
formed of semiconductor switching elements 12 and mounted to the
heat sink 32, the control board. 20 on which the microcomputer 16
generating drives signals of the semiconductor switching elements
12 and the drive circuit 19 are mounted, the sensor board 17 on
which the rotation sensor 16 detecting a rotation angle of the
rotor 24 is mounted, the smoothing capacitor 14 to remove a ripple
component from a motor current flowing to the electric motor 2, the
coil 15 to remove electromagnetic noises, a circuit case 34, and a
bus bar 35 electrically interconnecting the respective parts.
The rotation sensor 16 detects a rotation angle of the rotor 24 by
detecting an orientation of a magnetic field generated by the
sensor magnet 28. The rotation sensor 16 is disposed oppositely to
the sensor magnet 28, which is mounted to one end of the rotation
shaft 21, in the direction of the axis of rotation of the electric
motor. The rotation sensor 16 is mounted on the sensor board 17.
The sensor board 17 is fixed in a part of the heat sink 32 with
screws (not shown) or the like. The sensor board 17 and the control
board 20 are electrically connected via the bus bar 35. The
rotation sensor 16 is formed of a magneto-resistance effect element
(MR element), an anisotropic magneto-resistance layer element (AMR
element), a giant magneto-resistance effect element (GMR element),
or a tunneling magneto-resistance element (TMR element). The
rotation sensor 16 can be a single die, a dual die, or the
like.
A structure of the sensor magnet assembly 200 will now be
described. FIG. 3 is a plan view of the holder 29 of the first
embodiment along with a sectional view taken along the line A-A.
FIGS. 4A and 4B are plan views of the sensor magnet assembly 200 of
the first embodiment each along with a sectional view taken along
the line A-A. In the drawings, the holder 29 is made of a
non-magnetic material, such as SUS and aluminum. As is shown in
FIG. 3, the holder 29 includes a fit portion 36b for the rotation
shaft 21 formed in the direction of the axis of rotation. The fit
portion 36b has a cylinder shape with a non-circular cross section
formed of at least one plane 37b parallel to the axis of rotation
and a curved surface 39b connected to the plane 37b and concentric
with the axis of rotation. The fit portion 36b also has an end face
38b perpendicular to the axis of rotation in an inner part of the
holder 29 of a cylindrical shape. The end face 38b is provided with
a hole 40 penetrating through the holder 29 from inside to outside.
The hole 40 may be provided also to a surface other than the end
face 38b. For example, the hole 40 penetrating through the holder
29 from inside to outside may be provided to at least one of the
plane 37b and the curved surface 39b. An outer peripheral portion
41 of the holder 29 is substantially shaped like a cylindrical
pillar.
As is shown in FIGS. 4A and 4B, the sensor magnet 28 is integrally
molded with the holder 29 on the side of the end face 38b. The
sensor magnet 28 is formed continuously from inside to outside of
the holder 29 through the hole 40. Parts of the end face 38b, the
plane 37b, the curved surface 39b, and the outer peripheral portion
41 of the holder 29 are inside the sensor magnet 28. FIG. 4A shows
the holder 29 when the hole 40 is provided to the end face 38b and
FIG. 4B shows the holder 29 provided with the holes 40 in the end
face 38b and the plane 37b and the sensor magnet 28 molded
integrally with the holder 29.
Regarding a shape of the sensor magnet 28, the sensor magnet 28 has
an end face 38c perpendicular to the axis of rotation on a side
opposing the rotation sensor and an end face 38d perpendicular to
the axis of rotation on the side opposing the rotation shaft 21. A
shape of the sensor magnet 28 on an inner peripheral side of the
holder 29 is same as the shape of the fit poi-Lion 36b of the
holder 29. A shape of the sensor magnet 28 along the outer
peripheral portion 41 of the holder 29 can be a shape of a
cylindrical pillar or a rectangular pillar. However, the sensor
magnet 28 shaped substantially like a cylindrical pillar as shown
in FIGS. 4A and 4B is preferable because homogeneity of a magnetic
field can be secured.
The sensor magnet 28 is magnetized after the sensor magnet 28 is
integrally molded with the holder 29. The sensor magnet 28 is
positioned with respect to a magnetization yoke (not shown) using
the plane 37b and the curved surface 39b of the holder 29. The
sensor magnet 28 is positioned in a circumferential direction using
a positioning jig (not shown) of the magnetization yoke and the
plane 37b of the holder 29 and positioned in the radial direction
using the curved surface 39b. The sensor magnet 28 is an isotropic
magnet having a flux density of 0.4 to 0.8 [T] and a bond magnet is
preferable for the reason as follows. That is, when a flux density
is low, a clearance between the sensor magnet 28 and the rotation
sensor has to be reduced. In such a case, processing and assembly
accuracy is deteriorated and the sensor magnet 28 and the rotation
sensor may interfere with each other. Conversely, when a flux
density is high, a clearance has to be increased and a product size
is also increased.
In view of the foregoing, it is preferable to select neither a too
high nor too low flux density, that is, from 0.4 to 0.8 [T], as a
flux density of the sensor magnet 28.
A positioning method of the sensor magnet assembly 200 and the
rotation shaft 21 will now be described. FIG. 5 is a plan view of
the sensor magnet assembly 200 and the rotation shaft 21 along with
a sectional view taken along the line A-A when the rotation shaft
21 is mounted to the sensor magnet assembly 200.
As is shown in FIG. 5 and described above, the rotation shaft 21
has the fit portion 36a for the holder 29. The fit portion 36a is
formed of the plane 37a parallel to the axis of rotation, the end
face 38a perpendicular to the axis of rotation, and the curved
surface 39a concentric with the axis of rotation.
A positional relation of the sensor magnet assembly 200 relatively
with respect to rotation shaft 21 is as follows.
The sensor magnet assembly 200 and the rotation shaft 21 are
positioned in the circumferential direction by mounting the
rotation shaft 21 to the sensor magnet assembly 200 in such a
manner that the plane 37b of the holder 29 of the sensor magnet
assembly 200 and the plane 37a of the rotation shaft 21 become
parallel to each other. Herein, the plane 37b of the holder 29 of
the sensor magnet assembly 200 and the plane 37a of the rotation
shaft 21 are either in or out of contact with each other.
Also, the sensor magnet assembly 200 and the rotation shaft. 21 are
positioned in the radial direction by fitting the curved surface
39b of the holder 29 of the sensor magnet assembly 200 and the
curved surface 39a of the rotation shaft 21.
Further, the sensor magnet assembly 200 and the rotation shaft 21
are positioned in an axial direction by mounting the rotation shaft
21 to the sensor magnet assembly 200 in such a manner so as to
leave a slight gap g between the end face 38c of the sensor magnet
28 of the sensor magnet assembly 200 and the end face 38a of the
rotation shaft 21.
A fixing method of the sensor magnet assembly 200 and the rotation
shaft 21 will now be described FIG. 6 is a plan view showing a
dimensional relation of the sensor magnet assembly 200 and the
rotation shaft. 21 of this embodiment. FIG. 7 is a plan view of the
sensor magnet assembly 200 and the rotation shaft 21 of this
embodiment along with a sectional view taken along the line A-A
when the both are press-fit together. FIG. 8 is a sectional view of
the sensor magnet assembly 200 and the rotation shaft 21 of this
embodiment when the both are press-fit together and fixed by
caulking. FIG. 9 is a plan view of the sensor magnet assembly 200
and the rotation shaft 21 of this embodiment along with a sectional
view taken along the lane A-A when the both are fixed with an
adhesive.
The sensor magnet assembly 200 and the rotation shaft 21 can be
fixed by press-fitting or with an adhesive.
In the case of press-fitting, the fit portion 36b of the holder 29
has to be smaller than the fit portion 36a of the rotation shaft
21. More specifically, in FIG. 6, let Dh and Ds be minor diameters
of the holder 29 and the rotation shaft 21, respectively, and Lh
and Ls be distances from a center of the axis of rotation to the
planes 37a and 37b, respectively. Then, Dh<Ds and Lh<Ls are
given to enable the press-fitting. However, due to the presence of
the planes 37a and 37b, a deficiency, such as biting, is more
likely to occur in comparison with a case where circular portions
are press-fit together.
In such a case, by setting as: Dh<Ds and Lh>Ls, and fixing
the sensor magnet assembly 200 and the rotation shaft 21 by
press-fitting of the curved surfaces 39a and 39b alone, the
occurrence of press-fit biting can be suppressed. In such a case,
as is shown in FIG. 7, a clearance is generated between the planar
portion 37b of the holder 29 and the planar portion 37a of the
rotation shaft 21. When it is necessary to reduce the clearance, a
caulking portion 42 is provided as is shown in FIG. 8 after the
rotation shaft 21 is mounted to the sensor magnet assembly 200 by,
for example, applying a pressure to the plane 37b of the holder 29
to let plane 37b undergo deformation in the radial direction and
come into contact with the plane 37a of the rotation shaft 21.
In a case where the sensor magnet assembly 200 and the rotation
shaft. 21 are fixed with an adhesive, by setting as Dh>Ds and
Lh>Ls, an adhesive is interposed in a clearance generated
between the holder 29 and the rotation shaft 21 as is shown in FIG.
9. An adhesive 43 of FIG. 9 is made extremely thick for ease of
understanding.
According to this embodiment as above, positional accuracy in the
circumferential direction of the sensor magnet assembly 200 and the
rotation shaft 21 can be secured by using the planes 37a and 37b
and positional accuracy in the radial direction can be secured by
using the curved surfaces 39a and 39b. Accordingly, the rotation
shaft 21 and the sensor magnet can be positioned with high
accuracy. Consequently, detection accuracy of the rotation sensor
can be enhanced.
The sensor magnet assembly 200 and the rotation shaft 21 are fixed
by press-fitting or with an adhesive. In addition, the plane 37b of
the holder 29 of the sensor magnet assembly 200 and the plane 37a
of the rotation shaft. 21 engage with each other. Hence, rotations
of the sensor magnet assembly 200 about the axis of rotation can be
suppressed.
Further, the sensor magnet 28 is molded integrally with the holder
29 and the sensor magnet 28 is shaped so as to conform to the shape
of the fit portion 36b of the holder 29. Hence, rotations of the
sensor magnet 28 about the axis of rotation can be suppressed.
Consequently, reliability of the product can be enhanced. Moreover,
the manufacturing costs can be reduced because it is no longer
necessary to use an adhesive to fix the sensor magnet 28 to the
holder 29.
The sensor magnet 28 as a single member is present both in the
inside and the outside of the holder 29 through the hole 40. Hence,
the fixing strength of the sensor magnet 28 can be increased both
in the axial direction and in the circumferential direction.
Even in a case where the planar portions of the sensor magnet 28
and the holder 29 do not engage with each other, the magnet sensor
28 can be prevented from falling off from the holder 29 and also
from rotating by merely changing the position of the hole 40. By
providing a gap between the sensor magnet 28 and the rotation shaft
21, an amount of the magnet used for a reduction of leaking flux
can be reduced. Consequently, the manufacturing costs can be
reduced. Also, by providing the gap, a variation of the clearance
between the sensor magnet 28 and the rotation sensor can be reduced
because a tolerance of the respective parts forming the electric
motor no longer have influences on the clearance between the sensor
magnet 28 and the rotation sensor.
Because the holder 29 is made of a non-magnetic material, a leaking
flux during magnetization of the sensor magnet 28 after the sensor
magnet 28 is molded integrally with the holder 29 can be smaller.
Accordingly, the sensor magnet 28 can be magnetized fully at low
ampere-turns. Hence, a temperature of the magnetization coil rises
only moderately, a production time can be shorter, and the cost can
be reduced. By using an isotropic magnet having a residual flux
density of 0.4 to 0.8 [T] as the sensor magnet 28, a flux density
at a detection position can be changed by merely changing the
residual flux density without changing a shape of the sensor magnet
according to a board on which multiple rotation sensors 16 each
having different detection sensitivity can be mounted at different
positions. In addition, because the sensor magnet 28 is shaped like
a cylindrical pillar having planes at both ends, homogeneity of a
magnetic field can be secured.
By installing the electric motor with high detection accuracy of a
rotation angle as formed in this embodiment, the electric power
steering device 100 generating an adequate assist torque can be
obtained. Because the sensor magnet assembly 200 is formed of only
two parts, that is, the holder 28 and the sensor magnet, a
lightweight electric power steering device of a simple structure
capable of preventing a fall-off and rotations of the sensor magnet
without using an adhesive can be obtained. Moreover, because an
integrally-molded magnet is used, the electric power steering
device can be inexpensive, more fuel-efficient, and
safe-oriented.
Second Embodiment
A configuration and a structure of an electric motor and an
electric power steering device are same as those of the
counterparts of the first embedment above except for a sensor
magnet assembly 200.
The sensor magnet assembly 200 of this embodiment will be
described. FIG. 10 and FIG. 11 are plan views of the sensor magnet
assembly 200 of the second embodiment each along with a sectional
view taken along the line A-A.
In this embodiment, at least one plane 39d parallel to an axis of
rotation is provided to an outer peripheral portion 41 of a holder
29. The rest is same as the counterparts of the first embodiment
above.
According to this embodiment as described above, the planar portion
39d is provided to the outer peripheral portion 41 of the holder
29. Hence, rotations of a sensor magnet 28 about the axis of
rotation can be suppressed more steadily. By providing two planes
as shown in FIG. 10, the product becomes easy to hold and hence
ease of transportation can be enhanced.
In a case as shown in FIG. 11 where the plane 39d of the outer
peripheral portion 41 and a plane 37b of a fit portion 36h for a
rotation shaft 21 are parallel, that is, when the outer peripheral
portion 41 and the fit portion 36b are formed in a same shape, the
outer peripheral portion 41 and the fit portion 36b can be formed,
for example, by subjecting a thin plate to drawing using a pressing
machine. Consequently, the cost can be reduced in comparison with
cut processing.
Third Embodiment
A configuration and a structure of an electric motor and an
electric power steering device are same as those of the
counterparts of the first embedment above except for a sensor
The sensor magnet assembly 200 of this embodiment will be
described. FIG. 12 is a plan view of the sensor magnet assembly 200
of the third embodiment along with a sectional view taken along the
line A-A.
The sensor magnet assembly 200 is same as the counterpart in the
first embodiment above except for a protrusion 44 which is a part
of a holder 29 protruding in a direction of an axis of rotation
from an end face 38c of a sensor magnet 28.
According to this embodiment as above, the sensor magnet assembly
200 has the protrusion 44, which is a part of the holder 29
protruding in the direction of the axis of rotation from the end
face 38c of the sensor magnet 28. Hence, when the sensor magnet
assembly 200 is mounted to a rotation shaft 21 by, for example,
press-fitting, a direct application of a pressure to the sensor
magnet 28 can be avoided by pressing the protruding holder 29.
Accordingly, there can be achieved an effect that breaking and
chipping of the magnet can be suppressed.
DESCRIPTION OF REFERENCE NUMERALS AND SIGNS
1: steering wheel, 2: electric motor, 3: reduction device, 4:
control device, 5: battery, 6: torque sensor, 7: power connector,
8: vehicle-side signal connector, 9: torque sensor connector, 10:
armature winding, 11: stator, 12, 12a, and 12b: semiconductor
switching element, 13: shunt resistor, 14: smoothing capacitor, 15:
coil, 16: rotation sensor, 17: sensor board, 18: microcomputer, 19:
drive circuit, 20: control board, 21: rotation shaft, 22a and 22b:
bearing, 23: rotor magnet, 24: rotor, 25: frame, 26: housing, 27:
coupling, 28: sensor magnet, 29: holder, 30: insulator, 31: screw,
32: heat sink, 33: power circuit, 34: circuit case, 35: bus bar,
36a: fit portion of rotation shaft, 36b: fit portion of holder, 37a
and 37b: plane, 38a, 38b, 38c, and 38d: end face, 39a and 39b:
curved surface, 39d: plane, 40: hole, 41: outer peripheral portion,
42: caulking portion, 43: adhesive, 44: protrusion, 100: electric
power steering device, 200: sensor magnet assembly
* * * * *